A device for detecting an object by a statistic learning using a feature amount is disclosed, for instance, in Non-Patent Document 1 or Patent Document 1. The feature amount described in Non-Patent Document 1 is called Haar-like feature amount and obtained by the relation of the relative level of average luminance of pixels in one pair of block areas. FIG. 16 is a diagram for explaining one example (examples 1 and 2) of the feature amount described in Non-Patent Document 1. As shown in FIG. 16, in both the examples 1 and 2, when the relation of the relative level of the average luminance Aav and Bav of the pixels in the block areas of the one pair of blocks A and B shows a relation of Aav<Bav, the feature amount is set to P=0, and when the relation of the relative level of the average luminance Aav and Bav shows a relation of Aav≧Bav, the feature amount is set to P=1.
In the device disclosed in Non-Patent Document, the above-described Haar-like feature amount is used for a face detector to carry out learning by Boosting. The face detector includes a plurality of strong discriminators. Each of the strong discriminators has a high transmission rate to a face image and eliminates a non-face image by a prescribed value. Each of the strong discriminators has a plurality of weak discriminators. Each of the weak discriminators returns a score to the feature amount. The strong discriminator determines a face or a non-face depending on whether or not the total of the scores exceeds a threshold value. Each of the weak discriminators generates the feature amount from an input image of a prescribed size and returns the score for each feature amount to the strong discriminator by using the above-described Boosting learning result.
On the other hand, the feature amount described in Patent Document 1 is obtained by the relation of the relative level between an average luminance of pixels in block areas of all blocks A0 to A5 and an average luminance of pixels in each of the block areas. FIG. 17 is a diagram for explaining one example of the feature amount described in Patent Document 1. As shown in FIG. 17, when the relation of the relative level between the average luminance Aref of the pixels in the block areas of all the blocks A0 to A5 and the average luminance A0av to A5av of the pixels in each of the block areas shows a relation of Aiav (i=0 to 5)<Aref, the feature amount Pi is set to Pi (i=0 to 5)=0. When the relation of the relative level between the average luminance Aref and the average luminance A0av to A5av shows a relation of Aiav (i=0 to 5)≧Aref, the feature amount Pi is set to Pi(i=0 to 5)=1.